1. The Field of the Invention
This invention relates to antennas, more particularly to a portable antenna system wherein the radiating antenna elements and associated conductors are carried on reels for storage and transportation, and wherein the entire antenna system can be rolled out for rapid deployment and use.
2. The Prior Art
The design and manufacture of antennas for radiating radio-frequency electromagnetic waves has been the subject of ongoing research ever since "wireless" communication was first demonstrated. This research has continued to the point where, today, a multitude of different antennas are available for a wide variety of applications. Likewise, the design of radio-frequency transmitting and receiving equipment has also been the subject of extensive research and development. This research, and the general trend toward miniaturization of electronic components, has allowed the design and manufacture of compact, portable radio transmitters and receivers. Many of these transmitters and receivers are capable of being operated virtually anywhere. Presently available portable radio equipment ranges in size from small hand-held transceivers that may be easily carried by a single person, to large units, operated by batteries or a small generator, which are capable of transmitting thousands of watts of radio-frequency energy.
Portable transmitters and receivers have become indispensable in a wide variety of governmental and commercial applications. In particular, portable radio equipment has become an essential tool to police, rescue, and military organizations. For example, in military applications it is highly desirable to be able to move rapidly from one radio transmitting site to another as discretely as possible. Portable radio equipment available today generally is easily transported from one site to another. Antennas, as available previously in the art, however, have often been very difficult to move from site to site. Therefore, an antenna system which is compact and easily transportable, easily hidden, as well as operable in any weather or terrain, would be highly desirable. The antennas, however, that have been available in the art to the present time have generally presented several serious problems when used by organizations such as the military.
The problems encountered in the use of antenna designs found in the prior art stem from the fact that the available antennas which were reasonably portable were generally less efficient than was desirable. Thus, the antenna designer was faced with the choice of designing a very portable antenna or an efficient antenna. Alternatively, in some cases portability could be achieved but the antenna became extremely complex in its construction and deployment, or cumbersome in size and weight, and thus took a substantial period of time to set up as well as presenting other difficulties. An examination of the approaches taken in the prior art demonstrates the difficulties encountered in designing an antenna that is portable and that efficiently radiates and receives radio signals.
One approach taken in the prior art to provide an efficient portable antenna is to modify the design of a rigid-element antenna intended for use as a permanently installed antenna. This modification generally allowed the antenna to be disassembled for transportation from site to site. Furthermore, use of rigid elements in a portable antenna allows the antenna to be of a design similar to a permanently installed fixed-base antenna. Also, the use of a rigid-element antenna generally provides an antenna whose radiation pattern, directivity and standing wave ratio at a particular frequency, is independent of the physical surroundings in which it is operated. There are, however, several problems which accompany the use of rigid-element antennas for use as portable antennas.
The first of these problems is that assembly and disassembly of a rigid-element antenna generally takes a significant amount of time and can also be quite complex. The fact that the antenna takes an extended length of time to assemble or deploy reduces its usefulness with a portable transmitter/receiver. Second, rigid-element antennas, even when disassembled, are often both bulky and heavy, making them difficult to transport. Alternatively, if the weight of the rigid-element antenna is lessened to ease transportation difficulties, the rigid elements of the antenna generally become more fragile requiring greater care in assembly, disassembly, transportation, and use. Third, a rigid-element antenna generally requires suspension above the ground for proper operation. This is usually done by mounting the antenna on a tall mast. The requirement of a mast further increases the difficulty of transporting and assembling the antenna system in addition to providing a very conspicuous marking as to the location of the transmitter/receiver. Such conspicuousness can be a great disadvantage in a military operation. Fourth, the radiation pattern of rigid-element antennas generally cannot be altered easily. Altering the radiation patterns of such antennas generally requires the reorientation of the rigid elements in relation to one another or reorienting the position of the entire antenna system, as well as other system alterations, all of which can be difficult with rigid-element antennas. The above considerations all mitigate against the use of a rigid-element antenna for use with portable radio equipment.
Other types of antennas which have been used with portable radio equipment include single-element antennas often consisting of a single vertical element configured in a flexible "whip" manner. A single-element antenna provides some of the required portability, that is, ease of transportation and assembly, that is desired with portable radio equipment. Such antennas, however, have the drawback of not allowing a wide choice of radiation patterns and often are inefficient radiators and receivers of radio-frequency energy. While the above considerations are relevant to an antenna that is to be operated at any frequency, the above considerations become prominent in the design of an antenna that is to be operated in the high-frequency band, 3 MHz to 30 MHz, and lower frequency bands, such as the medium frequency band, 300 KHz to 3 MHz.
At high and medium frequencies it becomes especially difficult to design an efficient antenna that is still reasonably portable. This can be appreciated by understanding the considerations that apply when determining the necessary length of a half-wave radiating element that is to be operated at 30 MHz. The shortest length of an antenna element which will resonate at a given frequency must be approximately equal to one-half wavelength of that frequency. A 30 MHz signal has a wavelength of approximately 10 meters. Thus, a half-wave antenna must be approximately five meters in length. It can be appreciated that a rigid antenna element five meters in length can present considerable difficulties when transported. These problems are compounded when designing a portable antenna for use at frequencies lower than 30 MHz.
What is needed in the art is a portable antenna which is simple to transport and store as well as simple to deploy. Furthermore, it would be very advantageous to design a portable antenna which is capable of radiating high transit power efficiently as well as to allow easy alteration of the radiation pattern of the antenna. Still further, it would be an advancement in the art to design a portable antenna which is compact and lightweight and which is impervious to adverse weather conditions as well as easy to maintain.